This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Annual. Propagates by seeds.
Time of bloom: June to August.
Seed-time: July to September.
Range: Iowa, Illinois, Kansas, and Nebraska; also about Atlantic seaports. Habitat: Pastures, waste places.
The Caltrop is native to the Mediterranean regions of Europe, and is said to have been brought into its western range in the fleeces worn by imported sheep; and it is a very troublesome weed to wool-growers.
Stems eight inches to nearly three feet long, branching from the base, and often forking above, weak, slender, silky-hairy, some prostrate and others ascending, spreading on all sides. Leaves numerous, also silky-hairy, evenly pinnate, short-petioled, with ten to fourteen small, oblong, sessile leaflets, the pairs frequently unequal in size. Flowers axillary, on peduncles shorter than the leaves; they are about a half-inch broad, with five hairy, pointed, persistent sepals and five fan-shaped, rounded, yellow petals, broader than long, which soon fall away; stamens ten, as long as the petals; ovary five-celled and hairy, the styles united in a column with five-ridged stigma. The fruit, or nut, is nearly a half-inch broad, and splits at maturity into five carpels, each one armed with two to four hard, often curved and spreading spines. Each carpel contains several seeds, which, protected by their hard, spiny covering, may lie dormant in the soil for more than one season.
Fig. 182. - Alfilaria or Filaree (Erodium cicutarium). X 1/2.
Prevent seed production by close cutting before the first flowers mature. No annual plant can long survive which is not permitted to foul the ground with its future generations.